Susceptor for holding a semiconductor wafer having an orientation notch, a method for depositing a layer on a semiconductor wafer, and semiconductor wafer

ABSTRACT

A semiconductor wafer processing susceptor for holding a wafer having an orientation notch during deposition of a layer on the wafer, having a placement surface for supporting the semiconductor wafer in the rear edge region of the wafer, the placement surface having a stepped outer delimitation, and an indentation of the outer delimitation of the placement surface for placement of the partial region of the edge region of the rear side of the wafer in which the orientation notch is located onto a partial region of the placement surface delimited by the indentation of the outer delimitation of the placement surface. The susceptor is used in a method for depositing a layer on a wafer having an orientation notch, and wafers made of monocrystalline silicon upon which layers are deposited using the susceptor have greater local flatness on both front and rear sides proximate the orientation notch.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is Division of U.S. Ser. No. 15/260,629, filed Sep. 9,2016, (now pending), which claims priority to German Patent ApplicationNo. 10 2015 220 924.5 filed Oct. 27, 2015, the disclosures of which arehereby incorporated in their entirety by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The subject matter of the invention is a susceptor for holding asemiconductor wafer having orientation notch during the deposition of alayer on a front side of the semiconductor wafer. The susceptor has aplacement surface for placing the semiconductor wafer in the edge regionof a rear side of the semiconductor wafer and a stepped outerdelimitation of the placement surface. The subject matter of theinvention is also a method for depositing a layer on a semiconductorwafer having orientation notch, in which such a susceptor is used, and asemiconductor wafer made of monocrystalline silicon.

2. Description of the Related Art

Susceptors of the type mentioned are known in various embodiments. Anembodiment is described in DE 198 47 101 C1, in which the placementsurface is a component of a ring, which forms the susceptor. In theembodiment according to EP 1 460 679 A1, the susceptor additionally hasa bottom in the form of a plate. The placement surface is formed by aprojection on the plate edge. An embodiment is shown in DE 10 2006 055038 A1, in which the semiconductor wafer lies in a depression of a ring,and the ring lies on a base plate.

When depositing a layer on the front side of a semiconductor wafer,efforts are made, inter alia, to create a layer having uniform layerthickness and to have the usable surface of the layer extend as close aspossible to the edge of the semiconductor wafer. When attempting toimplement this specification, one is confronted with the problem thatflatness problems occur in the region of an orientation notch of thesemiconductor wafer, the causes of which are a greater layer thicknessand material deposits on the rear side of the semiconductor wafer. Toremedy this problem, it is proposed in US 2012/0270407 A1 and JP2013-51290 that the placement surface of the susceptor be enlargedinward at one point and the semiconductor wafer be laid on the susceptorsuch that the orientation notch comes to rest on the placement surfaceat this point.

US 2013/0264690 A1 relates to the improvement of the flatness of asemiconductor wafer having an epitaxial layer, in particular in the edgeregion of the semiconductor wafer. The local geometry in the edge regionof the front side, expressed by ESFQRmean and in consideration of anedge exclusion of 1 mm, is not greater than 100 nm.

Notwithstanding the cited prior art, the demand still exists forimproving the local flatness of a coated semiconductor wafer in theregion of the orientation notch.

SUMMARY OF THE INVENTION

It is the object of the present invention to propose a solution whichstrongly reduces an excess of the layer thickness in the region of theorientation notch and material depositions on the rear side of thesemiconductor wafer in the region of the orientation notch. These andother objects are achieved by a susceptor for holding a semiconductorwafer having orientation notch during the deposition of a layer on afront side of the semiconductor wafer;

a placement surface for placing the semiconductor wafer in the edgeregion of a rear side of the semiconductor wafer;

a stepped outer delimitation of the placement surface; and anindentation of the outer delimitation of the placement surface forplacement of the partial region of the edge region of the rear side ofthe semiconductor wafer in which the orientation notch is located, onthe partial region of the placement surface which is delimited by theindentation of the outer delimitation of the placement surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows typical features of a reactor, which is used in a methodfor depositing a layer on a semiconductor wafer.

FIG. 2 shows a susceptor designed according to the invention in a topview.

FIG. 3 shows an enlarged illustration of the region of the placementsurface of the susceptor according to FIG. 2, which is delimited by theindentation of the outer delimitation of the placement surface.

FIG. 4 shows the susceptor according to FIG. 2 and additionally asemiconductor wafer having orientation notch, which is placed on thesusceptor.

FIG. 5 shows an enlarged illustration of the region of the placementsurface of a susceptor which is delimited by the indentation of theouter delimitation of the placement surface, and additionally anindentation of the placement surface in this region.

FIG. 6 shows a material deposition on the rear side of a semiconductorwafer produced according to the invention in the region of theorientation notch and the height profile of the material depositionalong a line having a small distance to the apex of the orientationnotch.

FIG. 7 shows an illustration corresponding to FIG. 6 of a semiconductorwafer, which was not produced according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The indentation of the outer delimitation of the placement surface isoriented inward and preferably has a shape which is complementary to theshape of the orientation notch of the semiconductor wafer, which isplaced on the susceptor. The presence of the indentation of the outerdelimitation of the placement surface has the effect that a uniformdistance is ensured between an outer edge of the semiconductor wafer andthe outer delimitation of the placement surface. This distance isessentially identical in the region of the orientation notch and in theregion outside the orientation notch. This has an effect on the flowbehavior of a deposition gas. The flow picture is also essentiallyidentical in the region of the orientation notch and in the regionoutside the orientation notch. The material deposition is accordinglysubstantially uniform in the edge region of the semiconductor wafer.

The placement surface and the stepped outer delimitation of theplacement surface form a nearly circular pocket having nearly uniformdiameter for accommodating a semiconductor wafer having an orientationnotch. Because of the indentation of the outer delimitation of theplacement surface, the diameter of the outer delimitation of theplacement surface is smaller at this point than at the remaining points.

The radial width of the placement surface is the distance between theouter delimitation of the placement surface and an inner edge of theplacement surface. The radial width of the placement surface is muchless than the diameter which the outer delimitation of the placementsurface has outside the indentation. It is preferably not greater than10% of this diameter. The placement surface is sufficiently wide, on theother hand, to underlay a semiconductor wafer placed thereon completelyin the region of the orientation notch thereof, i.e., in the region ofthe indentation of the outer delimitation of the placement surface, theplacement surface has a radial width, as a result of which the placementsurface extends at least as far inward as an orientation notch of asemiconductor wafer lying on the placement surface in this region. Theaccess of deposition gas through the orientation notch to the rear sideof the semiconductor wafer is thus made more difficult.

The radial width of the placement surface is preferably uniform, i.e.,essentially the same in the region of the indentation of the outerdelimitation of the placement surface as outside this region. In thiscase, an inwardly oriented indentation of the placement surface isprovided in the region of the placement surface which is delimited bythe indentation of the outer delimitation of the placement surface.Notwithstanding this, it is also possibly provided that the placementsurface has a smaller radial width in the region of the indentation ofthe outer delimitation of the placement surface than outside thisregion.

The placement surface is arranged horizontally or inclined slopinginward somewhat. The angle of inclination is preferably not greater than3°. The profile of the inclination can be linear or curved.

The susceptor can be formed as a ring, comprising the placement surfaceand the outer delimitation of the placement surface. Furthermore, thesusceptor can be formed as a plate, additionally comprising adisk-shaped plate bottom, which lies adjacent to the inner edge of theplacement surface and lower than the placement surface. In addition, thesusceptor can also be formed in two parts, one part as a ring,comprising the placement surface and the outer delimitation of theplacement surface, the other part as a separate base plate, whichcarries the ring. The plate bottom or the base plate can begas-impermeable. However, it can also be formed perforated, to ensure agas transport through holes. A plate bottom or a base plate preferablyhas micropores instead of holes for such a gas transport. The microporescan be created, for example, in that fibers and/or particles arecompacted into the shape of the plate bottom or the base plate.

The susceptor preferably consists of silicon carbide or a material, forexample, graphite, which is coated using silicon carbide.

The subject matter of the invention is also a method for depositing alayer on a semiconductor wafer having orientation notch, characterizedby the placement of the semiconductor wafer on a susceptor according tothe invention, wherein the region of the edge region of the rear side ofthe semiconductor wafer, in which the orientation notch is located, isplaced on the region of the placement surface of the susceptor which isdelimited by the indentation of the outer delimitation of the placementsurface, and by the supply of a process gas to the front side of thesemiconductor wafer and the deposition of the layer on the front side ofthe semiconductor wafer.

The method results in improved flatness of the semiconductor waferhaving a deposited layer in the region of the orientation notch and moreuniform flatness in the edge region of the semiconductor wafer havingthe deposited layer.

After the placement of the semiconductor wafer on the susceptor, theedge of the semiconductor wafer, also in the region of the orientationnotch, essentially has an identical distance to the outer delimitationof the placement surface. If the indentation of the outer delimitationof the placement surface were absent, this distance would be greater inthe region of the orientation notch than outside this region. Because ofthe greater distance, more material would be deposited in the region ofthe orientation notch than outside this region, because as a result ofthe greater distance, a larger quantity of deposition gas reaches theedge region of the front side of the semiconductor wafer. Depositions inthe edge region of the rear side of the semiconductor wafer behavesimilarly. Greater distances of the edge of the semiconductor wafer tothe outer delimitation of the placement surface result in strongercoating of the rear side of the semiconductor wafer in the region of theorientation notch. This effect is particularly pronounced if theplacement surface is inclined sloping inward and/or the susceptorconsists of a porous material, which is permeable to the deposition gas,and/or the plate bottom or the base plate is provided with regularlyarranged holes, which make the access of deposition gas to the rear sideof the semiconductor wafer easier.

The method is preferably used for depositing an epitaxial layer on amonocrystalline semiconductor wafer, particularly preferably fordepositing an epitaxial layer made of silicon on a semiconductor wafermade of monocrystalline silicon. The semiconductor wafer made ofmonocrystalline silicon preferably has a diameter of not less than 200mm, particularly preferably a diameter of not less than 300 mm. Thethickness of the epitaxial layer is preferably not less than 1.5 μm andnot greater than 5 μm.

The subject matter of the invention is also the product of such amethod, namely a semiconductor wafer made of monocrystalline siliconhaving a diameter, a front side, a rear side, an edge region, anorientation notch in the edge region, and an epitaxial layer made ofsilicon on the front side, wherein the epitaxial layer has a thicknessof not less than 1.5 μm and not greater than 5 μm, characterized by alocal flatness of the semiconductor wafer in the region of theorientation notch, expressed by ESFQR, of not less than 5 nm and notgreater than 20 nm.

ESFQR is a parameter which describes the local flatness of 72 sectors inthe edge region of the front side of the semiconductor wafer. A sectorhas a width of 5° and a radial length of 30 mm. According to theinvention, the sector in which the orientation notch is located has alocal flatness ESFQR of not less than 5 nm and not greater than 20 nm,wherein an edge exclusion (EE) of 1 mm and a rectangular exclusionwindow around the orientation notch (notch exclusion window) remainunconsidered in the determination of the ESFQR. The rectangularexclusion window is centrally above the orientation notch and has awidth of 4 mm and a height of 2.5 mm. The height extends from thecircumference of the semiconductor wafer along the middle of theorientation notch.

The thickness of material deposition on the rear side of thesemiconductor wafer, on a rectangular evaluation area enclosing theorientation notch, is preferably not greater than 15 nm. The evaluationarea is located centrally above the orientation notch and has a width of8 mm and a height of 3.5 mm. The height extends along the center of theorientation notch and has a distance from 0.5 mm to the circumference ofthe semiconductor wafer. The circumference of a circle having the centerof the semiconductor wafer as the center of the circle and having thediameter of the semiconductor wafer is the circumference of thesemiconductor wafer. The center of the orientation notch extends fromthe apex of the orientation notch radially up to the circumference ofthe semiconductor wafer. The apex of the orientation notch is located atthe location of the orientation notch having the smallest distance tothe center of the semiconductor wafer.

The invention will be described in greater detail hereafter on the basisof drawings and an example.

The reactor according to FIG. 1 comprises a chamber having an upper dome1, a lower dome 2, and a side wall 3. The upper and lower domes 1, 2 aretransparent to thermal radiation, which is emitted from a radiant heaterarranged above and below the chamber. The layer is deposited from thegas phase on the front side of the semiconductor wafer 4, in thatdeposition gas is conducted over the front side of the heatedsemiconductor wafer and reacts at this time with the surface of theexposed front side while forming the layer. The lateral surface of thesemiconductor wafer, on which one intends to deposit the layer, isreferred to as the front side. This is typically a polished lateralsurface of the semiconductor wafer in this case. Due to the depositionof the layer, the semiconductor wafer receives a new front side, whichis formed by the free surface of the layer. The deposition gas issupplied through a gas inlet in the side wall of the chamber and theexhaust gas remaining after the reaction is discharged through a gasoutlet in the side wall of the chamber. Embodiments of the chamber areknown which have a further gas inlet and a further gas outlet. Suchembodiments are used, for example, to introduce and discharge flushinggas into and out of the volume of the chamber present below thesemiconductor wafer.

During the deposition of a layer, the semiconductor wafer is held by asusceptor 5 and rotated together with the susceptor about its center.

FIG. 2 shows a susceptor according to the invention in a top view. Thesusceptor 5 comprises a placement surface 6 for the placement of asemiconductor wafer in the edge region of a rear side of thesemiconductor wafer and a stepped outer delimitation 7 of the placementsurface. The placement surface extends from the stepped outerdelimitation 7 up to an inner edge 9 of the placement surface. Thesusceptor 5 has the shape of a plate having a bottom 8. The bottom 8 isarranged lower than the placement surface 6. The stepped outerdelimitation 7 has an inwardly oriented indentation 10. The indentation10 is approximately V-shaped and therefore shaped complementary to theshape of the orientation notch of a semiconductor wafer. The diameter dof the outer delimitation 7 of the placement surface outside the regionof the indentation 10 is greater than the diameter of a semiconductorwafer to be placed.

It can be seen in the enlarged illustration according to FIG. 3 that theplacement surface of the illustrated embodiment is less wide in theregion of the indentation 10 than outside this region.

FIG. 4 shows the susceptor 5 according to FIG. 2 having a semiconductorwafer 11 placed thereon having orientation notch 12. The semiconductorwafer 11 is located in the edge region of the rear side thereof on theplacement surface 6, in such a way that the region of the edge region ofthe rear side of the semiconductor wafer in which the orientation notch12 is located is placed on the region of the placement surface 6 whichis delimited by the indentation 10 of the outer delimitation.

FIG. 5 shows an enlarged illustration of the region of the indentation10 of the outer delimitation of the placement surface of a susceptor,the embodiment of which is particularly preferred. The placement surface6 is the same width in the region of the indentation 10 as outside thisregion. As a result of this, an inwardly oriented indentation 13 of theplacement surface 6 is also provided in this region

Example and Comparative Example

Semiconductor wafers made of monocrystalline silicon having a diameterof 300 mm were coated in a reactor according to FIG. 1 with a 2.5 μmthick epitaxial layer made of silicon. Subsequently, the local flatnessESFQR of the sector having the orientation notch was determined by meansof a measuring device of the type WaferSight of the producer KLA-TencorCorporation and the topography of the rear side in the region of theorientation notch was studied by means of a confocal microscope.

During the deposition of the epitaxial layer, the semiconductor wafersaccording to the example were laid in the edge region of the rear sidethereof on a susceptor according to the invention having the featuresshown in FIG. 5 in the region of the indentation of the outerdelimitation of the placement surface. The indentation of the outerdelimitation and the orientation notch of the semiconductor wafer werearranged in relation to one another as shown in FIG. 4.

In contrast, semiconductor wafers according to the comparative examplewere laid during the deposition of the epitaxial layer on a susceptorhaving the features described in US 2012/0270407 A1. The orientationnotch was underlaid by the projection of the placement surface showntherein

The ESFQR in the sector having the orientation notch was not greaterthan 20 nm, at best not greater than 10 nm, with an edge exclusion of 1mm, in the semiconductor wafers according to the example.

In contrast, in the semiconductor wafers according to the comparativeexample, the ESFQR in the sector having the orientation notch was notless than 40 nm.

FIG. 6 and FIG. 7 show the topography and the height profile of materialdepositions on the rear side in the region of the orientation notch of asemiconductor wafer having epitaxial coating according to the example(FIG. 6) and comparative example (FIG. 7). Note the different scales ofthe vertical axes.

Optical evaluation using a confocal microscope shows, in the case of thesemiconductor wafer according to the example, almost no shadow in theregion of the orientation notch (FIG. 6), while in contrast, in the caseof the semiconductor wafer according to the comparative example, ashadow which indicates a material deposition in this region is clearlyrecognizable (FIG. 7).

In both cases, the associated height profile of the material depositionwas determined along a line 14, which had a distance of 1 mm to the apex15 of the orientation notch of the respective semiconductor wafer. Theline was selected because the evaluation in the confocal microscopecaused it to be expected that the material deposition will have thegreatest thickness within the evaluation area there.

The greatest thickness of the material deposition was hardly greaterthan 10 nm in the case of the semiconductor wafer according to theexample (FIG. 6), but was greater than 700 nm in the case of thesemiconductor wafer according to the Comparative Example (FIG. 7).

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method for depositing a layer on asemiconductor wafer having an outer edge and having an orientationnotch, comprising: a) placing the wafer on a susceptor during thedeposition of a layer on a front side of the semiconductor wafer, thesusceptor comprising: a)i) a placement surface for receiving thesemiconductor wafer in an edge region of a rear side of thesemiconductor wafer, the placement surface having an inner diameterwhich is smaller than the diameter of the wafer; a)ii) an upwardlystepped outer delimitation of the placement surface forming a circularwafer-receiving pocket; a)iii) a radially inward protrusion of theupwardly stepped outer delimitation of the placement surface aroundwhich the orientation notch of a wafer is to be placed, configured suchthat the protrusion is in a spaced relationship with the waferorientation notch; and a)iv) a radially inward protrusion of theplacement surface in a region of the radially inward protrusion of theupwardly stepped outer delimitation of the placement surface, whereinthe wafer is placed onto the susceptor such that a partial region of theedge region of the rear side of the semiconductor wafer in which theorientation notch is located is on the radially inward protrusion of theplacement surface; b) supplying a process gas to the front side of thesemiconductor wafer while rotating the susceptor; and c) depositing thelayer on the front side of the semiconductor wafer, wherein the upwardlystepped outer delimitation surface of the susceptor and the radiallyinward protrusion thereof are configured to receive a semiconductorwafer having an orientation notch so as to provide a uniform distancebetween all portions of the wafer including its orientation notch andthe upwardly stepped outer delimitation of the placement surface.
 2. Themethod of claim 1, wherein a top surface of the susceptor which extendsradially outward from the upwardly stepped outer delimitation of theplacement surface, is uniformly flat.
 3. The method of claim 1, whereinan epitaxial layer is deposited on the front side of the semiconductorwafer.
 4. The method of claim 1, wherein an epitaxial layer comprisingsilicon is deposited on a monocrystalline semiconductor wafer comprisingsilicon, the thickness of the epitaxial layer being not less than 1.5 μmand not greater than 5 μm.
 5. The method of claim 1, wherein theplacement surface is arranged horizontally.
 6. The method of claim 1,wherein the placement surface is not horizontal, but is arranged slopinginward, with an angle of inclination not greater than 3°.
 7. The methodof claim 1, wherein the radially inward protrusion of the placementsurface extends at least as far radially inward as the orientation notchof the wafer after placement of the semiconductor wafer onto thesusceptor.
 8. The method of claim 1, wherein the susceptor has a singleradially inward protrusion of the upwardly stepped delimitation of theplacement surface and a single radially inward protrusion of theplacement surface in the region of the radially inward protrusion of theupwardly stepped outer delimitation of the placement surface.
 9. Themethod of claim 1, wherein the susceptor has a bottom plate below thewafer, the bottom plate containing micropores.
 10. The method of claim6, wherein the sloped placement surface has a curved profile.